diff --git a/requirements.txt b/requirements.txt
index c03d5b1d..7c8df363 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 pbr>=0.5.21,<1.0
 argparse
 httplib2
-iso8601>=0.1.4
+iso8601>=0.1.4,!=0.1.5,!=0.1.6
 PrettyTable>=0.6,<0.8
 python-keystoneclient>=0.4.1